Fragmentation of underground metallic silos subjected to internal blast



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United States Patent FRAGMENTATION 0F UNDERGROUND METAL- LIC SlLOSSUBJECTED T0 INTERNAL BLAST Jens C. Dolling, Morris Plains, N.J.,assignor, by mesne assignments, to the United States of America asrepresented by the Secretary of the Army Filed Jan. 24, 1967, Ser. No.611,482 Claims. (Cl. 220--18) This invention relates to undergroundstorage containers subjected to accidental detonation of explosiveswhere controlled fragmentation is desirable and particularly tounderground metallic silos subjected to internal blast.

Underground metallic silos are used as explosive storage containers.Their proximity to inhabited areas commands a safety zone around them incase of an accidental in-container explosion. As the sites may belocated in heavily populated districts, real estate costs could prove tobe quite high. Therefore, the greatest possible reduction in safety zoneradius is desirable.

The size of the safety zone radius is mainly a function of both theoverpressure generated by an explosion and the accompanying debrisformed.

For the case of circular cylindrical metal containers placed aboveground and used as explosive storage containers, standard tables areavailable to determine the safety zone radius. This radius, of course,satisfies both the overpressure and debris requirements.

The use of a barricade at least as high as the explosive storagecontainer and at least a minimum and less than a maximum distance awayhas long been employed to reduce the safety zone radius. However, it isdesirable to reduce the safety zone radius even more.

In the case of underground emplacement, the designer can consider thecontainer as being underground at all times. This is because theexplosive is above ground for an appreciable length of time only at atest site or in a war situation. At a test site, land is in abundanceand the lowering of the safety zone radius is not a basic consideration.In a war situation, ordinary safety considerations are disregarded.

Accordingly, the principal object of this invention is to produce animproved design for underground cylindrical containers which willprevent flying debris and minimize overpressure in case of anin-container explosion.

A particular object of this invention is to provide a container havingmeans for directing the forces resulting from an explosion of materialenclosed in the container.

Another particular object of this invention is to provide a containerwhich will rupture along predetermined lines instead of disintegratinginto fragments.

Other objects and many of the attendant advantages of this inventionwill be appreciated more readily as the same becomes understood byreference to the following detailed description, when considered inconnection with the accompanying drawing, wherein:

FIGURE 1 is an elevational view of an ordinary cylindrical silo;

FIGURE 2 is an elevational view of an alternative embodiment of thisinvention;

FIGURE 3 is an elevational view of the preferred embodiment of thisinvention;

FIGURE 4 is an elevational view of another alternative embodiment ofthis invention;

3,404,797 Patented Oct. 8, 1968 FIGURE 5 is an elevational view ofanother alternative embodiment of this invention;

FIGURE 6 is an elevational view of a modified cylindrical silo;

FIGURE 7 is .an elevational view of another modified cylindrical silo;and

FIGURE 8 is an elevational view of still another modified cylindricalsilo.

The apparatus of this invention achieves the direction of the forcesresulting from an explosion and the consequent rupturing alongpredetermined lines by means of sudden changes of thickness of thecylindrical container in a longitudinal (parallel to the cylinder axis)direction.

Referring now to FIGURES 1 through 8, FIGURE 1 shows an ordinarycylindrical silo 8 of the prior art. It is a thin cylindrical shell ofuniform thickness. A fiat bottom plate 10 is shown attached to thebottom of the shell.

FIGURE 2 shows an alternative embodiment of a cylindrical silo 8' ofthis invention. The sudden changes in cylinder wall thickness areachieved by means of Iongitudinal rows of drilled holes (cavities) 12 ofdesired size, depth, and spacing. Other methods such as slitting canalso be used. Preferably, eight longitudinal rows are employed, as inthis embodiment. In the event of an explosion, the ripping occurs alongthese rows of cavities, no loose fragments are generated and thegenerated strips hang to the bottom plate 10.

FIGURE 3 shows the preferred embodiment of a cylindrical silo 8' of thisinvention. A top cover 14 is employed. A top cover is not required, butif used, the top portion of the cylinder should have a tie-in to the topcover without undue stress concentration. Thus, the explosive gaspressure will not tear the cover oflt before stresses have caused it toopen in longitudinal cracks and release gas pressure into the soil. Thepreferred embodiment of this invention employs a top cover having acentral hole 16 and from Where structurally weakened por' tions 18radiate to the intersection of respective rows 12 with the upper end ofthe cylinder.

Similar considerations as applied to the top cover of the cylinderapplies to a bottom cap. If a bottom cap 10' is used (as in thepreferred embodiment of this invention), it should connect with acylindrical portion of its own onto the cylindrical shell. Thiscylindrical portion of the bottom cap 10 should change into anapproximately ellipsoidal shape further down. Preferably, thisellipsoidal end should have a flat central area. Thus, plastic hingingalong rows 12 of silo 8' is achieved. This shape is preferred, althoughalmost any concave upwards shape can be used.

Such an end cap may be used in the preferred embodiment or combined withany of the alternative embodiments of this invention. If used, it issubstituted for end plate 10.

FIGURE 4 shows an alternative embodiment of this invention employingreinforcing bars 20 extending longitudinally along a cylindrical silo8'. Such a bar may be part of the silo itself and accordingly is definedherein to include. such.

FIGURE 5 shows an alternative embodiment of this invention employing tworeinforcing bars 20' extending longitudinally along cylindrical silo 8',and rows of drilled holes 12 (only one shown) extending longitudinallyalong cylindrical silo 8'. This combination of weakening and--strengthening in the same cylindrical silo has been found to produceoptimum results for the case of a cylindrical silo without a top cover.Preferably, in this alternative embodiment, the drilled holes andparallel reinforcing bars are in alternate positions around the silo.

FIGURE 6 shows a cylindrical silo 8 employing reinforcing rings 22latitudinally placed and a top plate 23 that is secured in aconventional manner such as by bolts (not shown) to the top reinforcingring.

FIGURE 7 shows a cylindrical silo 8" employing a reinforcing ring 22connected by a reinforcing bar 24 to an anchoring member 26.

FIGURE 8 shows a cylindrical silo 8" employing latitudinally placed,structurally weakened ring portions 28.

The structures 8" in FIGURES 6-8, employing sudden changes in thicknesslatitudinally, all proved unsuccessful, contrary to expectations.

From the viewpoint of minimization of debris and overpressure, thetechnically optimum container will have to look pretty much like acylindrical pressure vessel with one or two dished end plates, of whichthe upper one contains a central hole, from which structurally weakenedportions radiate. This is the preferred embodiment of this invention.

The apparatus of this invention can be utilized in any case of anunderground container subject to accidental detonation where controlledfragmentation is desirable.

What is claimed is:

1. A silo for use underground in storing explosives, said silocomprising a cylindrical metal container having longitudinal rows ofsudden changes of thickness with each row extending in a directionparallel to the axis of said container, said rows being generallyequally spaced apart about the circumference of said cylindrical metalcontainer whereby when suflicient force is applied internally of saidcylindrical container, said cylindrical container will rupture alongpredetermined lines to form strips.

2. A silo as set forth in claim 1 wherein said sudden changes ofthickness comprise reinforcing bar means along said container.

3. A silo as set forth in claim 2 wherein said sudden changes ofthickness further include at least one structur- 4. ally weakenedportionalong said container, said structurally weakened portion being parallelto said reinforcing bar means.

4. A silo as set forth in claim 1 wherein said sudden changes ofthickness comprise a first plurality of structurally weakened portionsand a second plurality of reinforcing bar means, and wherein saidreinforcing bar means and said structurally weakened portions alternatearound said container. 4

5. A silo as set forth in claim 4 wherein said first plurality and saidsecond plurality each equal two.

6. A silo as set forth in claim 1 wherein said sudden changes inthickness comprise structurally weakened portions along said container.

7. In combination with a silo as set forth in claim 6,

'a top cover attached to the upper end of said silo, said top coverhaving structurally weakened portions emanating from the center of saidtop cover and approximately intersecting respective ones of saidstructurally weakened portions of said container approximately at saidupper end of said silo, in order to minimize fragmentation and causerupturing along predetermined lines approximating said structurallyweakened portions of said top cover and said silo in case of anexplosion.

8. In combination with a silo as set forth in claim 7, a bottom capattached to the lower end of said silo, said bottom cap being shapedconcave upwards.

9. A silo as set forth in claim 1 wherein said sudden changes inthickness comprise structurally weakened portions along said container,and a bottom cap attached to the lower end of said silo, said bottom capbeing shaped concave upwards.

10. In combination with a silo as set forth in claim 1, a bottom plateattached to the lower end of said silo.

References Cited UNITED STATES PATENTS 3,038,627 6/1962 Daley 220-893,166,829 1/1965 Lemelson 22072 3,225,953 12/1965 Wolfe 22018 JAMES B.MARBERT, Primary Examiner.

1. A SILO FOR USE UNDERGROUND IN STORING EXPLOSIVES, SAID SILOCOMPRISING A CYLINDRICAL METAL CONTAINER HAVING LONGITUDINAL ROWS OFSUDDEN CHANGES OF THICKNESS WITH EACH ROW EXTENDING IN A DIRECTIONPARALLEL TO THE AXIS OF SAID CONTAINER, SAID ROWS BEING GENERALLYEQUALLY SPACED APART ABOUT THE CIRCUMFERENCE OF SAID CYLINDRICAL METALCONTAINER WHEREBY WHEN SUFFICIENT FORCE IS APPLIED INTERNALLY OF SAIDCYLINDRICAL CONTAINER, SAID CYLINDRICAL CONTAINER WILL RUPTURE ALONGPREDETERMINED LINES TO FORM STRIPS.